1. Field of the Invention
The present invention relates to a structure for fitting a piezoelectric element to an object and a head suspension provided with such a structure, the piezoelectric element deforming in response to a voltage applied thereto and thereby moving an object.
2. Description of Related Art
Small-sized, precision information devices are rapidly advancing, and for use with such devices, needs for micro-actuators capable of conducting positioning control for very small distances are increasing. Such micro-actuators are highly needed by, for example, optical systems for correcting focuses and inclination angles, ink-jet printers for controlling ink heads, and magnetic disk drives for controlling magnetic heads.
The magnetic disk drives increase storage capacity by increasing the number of tracks per inch (TPI), i.e., by narrowing the width of each track on a magnetic disk.
Large-capacity magnetic disk drives, therefore, need an actuator capable of precisely positioning the magnetic head within a minute range across tracks.
To meet the need, Japanese Unexamined Patent Application Publication No. 2002-184140 discloses a head suspension with a dual actuator system. The dual actuator system employs a piezoelectric element in addition to a usual voice coil motor that drives a carriage to which the head suspension is attached. The piezoelectric element is arranged between a base plate and a load beam of the head suspension, to minutely move a magnetic head attached to a front end of the load beam.
According to this related art, the voice coil motor turns the head suspension through the carriage, and in addition, the piezoelectric element deforms in proportion to a voltage applied thereto, to minutely move the magnetic head at the front end of the load beam in a sway direction (a widthwise direction of the load beam) relative to the base plate. The dual actuator system involving the voice coil motor and piezoelectric element is capable of precisely positioning the magnetic head to a target position on a magnetic disk.
The head suspension with the dual actuator system employs a structure for fitting the piezoelectric element to an actuator base of the head suspension.
The actuator base has an opening to accommodate the piezoelectric element and a receiver that protrudes inwardly from an inner circumferential edge of the opening to support the periphery of the piezoelectric element.
When the piezoelectric element is set in the opening of the actuator base, a liquid adhesive is applied and solidified between the piezoelectric element and the receiver and inner circumferential edge of the opening, thereby attaching the piezoelectric element to the actuator base. To surely fix the piezoelectric element to the actuator base, the liquid adhesive is applied so that it slightly swells out of the receiver into a hole defined by an inner end of the receiver.
With this, the piezoelectric element is surely bonded to the actuator base, to secure electric insulation between them and effectively transfer deformation (driving force) of the piezoelectric element through the actuator base to the load beam.
To deform the piezoelectric element attached in that way, a voltage is applied through a flexure (wiring member) that is arranged on the actuator base.
According to the related art, a part of the flexure protrudes from the inner end of the receiver to the hole defined by the inner end of the receiver and faces the piezoelectric element through the hole. The protruding part of the flexure may come in contact with the swelled part of the liquid adhesive.
If this happens, the swelled part of the liquid adhesive is drawn from the receiver into the hole due to a capillary phenomenon of the liquid adhesive between the flexure and the piezoelectric element.
Generally, the liquid adhesive is continuously applied in a given quantity to the receiver and inner circumferential edge of the opening. If the liquid adhesive is drawn into the hole due to the capillary phenomenon, the adhesive left between the piezoelectric element and the receiver and inner circumferential edge of the opening will be insufficient and will deteriorate bonding strength between the piezoelectric element and the actuator base.
This results in incorrectly transferring deformation (driving force) of the piezoelectric element to the actuator base and unexpectedly increasing the rigidity of the hole to worsen the dynamic characteristics of the head suspension.